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The PP engine CAN deliver good SFC *IF* tuned appropriately. There's the rub. If tuned for good SFC at max output, it won't be too good at lower rpm. Unfortunately, we don't run at max output most of the time (in cruise). That's where the Renesis shines. It will deliver good SFC all across it's operating range and do it with mostly off the shelf hardware.
The conservative timing small runners and throttle in rotor housing on the Powersport engine was a good attempt at working around this problem. But the same performance can be had with the sideport 13B with the minor disadvantage of a higher RPM operating point. A higher gear ratio fixes that inexpensively (cost about the same as lower ratio).
Two factors would help the PP engine. Variable tuned manifold and a good CS prop. This is a good arguing point but for most builders this is not an option. Time, fabricating skills and money limitations have turned many projects into "Garage Art" rather than flying aircraft. The potential of the PP engine is real but know what you are getting into before making your plans.
Tracy (still buried with updates)
From: "Ed Anderson" <eanderson@carolina.rr.com>
Reply-To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: [FlyRotary] BSFC was [FlyRotary] Re: Fw: Different Rotary Port configurations
Date: Tue, 19 Jun 2007 08:26:05 -0400
Ok, Bill, I think we agreed that a stock Renesis could be cheaper than a PP (all depending on price paid for either, of course).
However, I'm not certain I fully understood whether my comment about the Renesis betting a better specific Fuel consumption than a PP was an area of disagreement. It appears it was.
I must admit some degree of ignorance in this area , however, I always thought that getting better SFC was due (at least in part) better use of each unit of fuel to produce useful mechanical work. So, if I understood you correctly, you are saying that the PP which has all this overlap gets a better SFC than the Renesis which can better contain the combustion process (no overlap). I must admit that surprises me. But, always willing to learn.
ED
----- Original Message -----
From: WRJJRS@aol.com
To: Rotary motors in aircraft
Sent: Tuesday, June 19, 2007 1:19 AM
Subject: [FlyRotary] Re: Fw: Different Rotary Port configurations
In a message dated 6/18/2007 4:30:46 PM Pacific Standard Time, eanderson@carolina.rr.com writes:
Renesis will undoubtedly get a better specific fuel consumption than a PP.
So for those that want the utmost in power, it sounds like the PP is the
way to go. For other cheap old chaps the Renesis would appear to offer a
cost effective power increase.
Ed
Here Ed I have to totally DISagree. The side ported engine is used to provide more power, and has bigger side ports only workable with the Renesis, but must also pass smog regulations and provide low-end torque for car use. The need for the higher redline is the total giveaway. For ANY i.c.e. the key to higher bmep is higher RPM. Spin your 13B to 9k and provide it with an adaquate intake and exhaust I would bet money you will be within a few HP. While I don't want to sound like a broken record, and certainly not trying to be contentious, Mazda built the 26B for use in a race using an economy formula. If side ports were more efficient they would have used them! P-ports make more power, but in the low to midrange so critical in a car they are much dirtier on HC. I really believe that the Renesis came from Mazda's hydrogen experiments. The ability to produce large ports WITH NO OVERLAP was critical to the success of that project. Much talk has been made of the fact that p-port rotaries have considerable overlap in the exhaust to intake phase. So does every high performance piston engine ever built. Tuners have even found the overlap phase to be beneficial to performance when the engine is properly tuned. The reason for the renesis is IMHO the need to pass smog and provide competitive power, Not that the Renesis is the "best" configuration. I'm glad they're building it since it is the key to Rotary survival. I simply harbor no delusions that Mazda wouldn't run a p-port with variable length intake tract if smog and noise would allow it. The advent of truly functional Direct injection may make the return of p-ports possible, but there is now a lot of inertia against them.
As for cheaper I agree. Anything over-the-counter is a less expensive solution!
Bill Jepson
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